Phosphine-ligated Ir(III)-complex as a bi-functional catalyst for one-pot tandem hydroformylation-acetalization

Article abstract of DOI:10.1016/j.jcat.2019.04.004

The complexation of IrCl₃?3H₂O with the electron-deficient phosphines (L1-L6) respectively afforded a bi-functional catalyst possessing the dual functions of transition metal complex (Ir^III-P) and Ir^III-Lewis acid for tandem hydroformylation-acetalization of olefins. The best result was obtained over L5-based IrCl₃?3H₂O catalytic system which corresponded to 97% conversion of 1-hexene along with 92% selectivity to the target acetals free of any additive. The crystal structure of the novel Ir^III-complex of Ir^III-L4 indicated that the electron-deficient nature of the involved phosphine warranted Ir-center in +3 valence state without reduction, which served as the Lewis acid catalyst for the subsequent acetalization of the aldehydes as well. Moreover, as an ionic phosphine, L6-based IrCl₃?3H₂O system immobilized in RTIL of [Bmim]PF₆ could be recycled for 6 runs without the obvious activity loss or metal leaching.

Full text of DOI:10.1016/j.jcat.2019.04.004

Journal of Catalysis 373 (2019) 215–221
Contents lists available at ScienceDirect
Journal of Catalysis
journal homepage: www.elsevier.com/locate/jcat
Phosphine-ligated Ir(III)-complex as a bi-functional catalyst for one-pot
tandem hydroformylation-acetalization
⇑
Huan Liu, Lei Liu, Wen-Di Guo, Yong Lu, Xiao-Li Zhao, Ye Liu
Shanghai Key Laboratory of Green Chemistry and Chemical Processes, School of Chemistry and Molecular Engineering, East China Normal University, Shanghai 200062, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
The complexation of IrCl3Á3H2O with the electron-deficient phosphines (L1-L6) respectively afforded a bi-
functional catalyst possessing the dual functions of transition metal complex (IrIII-P) and IrIII-Lewis acid
for tandem hydroformylation-acetalization of olefins. The best result was obtained over L5-based
IrCl3Á3H2O catalytic system which corresponded to 97% conversion of 1-hexene along with 92% selectivity
to the target acetals free of any additive. The crystal structure of the novel IrIII-complex of IrIII-L4 indi-
cated that the electron-deficient nature of the involved phosphine warranted Ir-center in +3 valence state
without reduction, which served as the Lewis acid catalyst for the subsequent acetalization of the alde-
hydes as well. Moreover, as an ionic phosphine, L6-based IrCl3Á3H2O system immobilized in RTIL of
[Bmim]PF6 could be recycled for 6 runs without the obvious activity loss or metal leaching.
Ó 2019 Published by Elsevier Inc.
Received 7 January 2019
Revised 29 March 2019
Accepted 1 April 2019
Keywords:
Hydroformylation
Acetalization
Tandem reaction
Iridium complex
Bi-functional catalyst
Co-catalysis
Electron-deficient phosphine
1. Introduction
to produce aldehydes [2,12,13], and the Lewis/ Brønsted acid cata-
lyst is in charge of the subsequent acetalization of the aldehydes to
Hydroformylation, the addition of synthesis gas (CO/H2) to ole-
fins, is one of the most important homogeneously catalyzed pro-
cesses for the production of aldehydes in industrial scale [1–4].
In many cases, aldehydes are not the final products and can further
convert into alcohols, esters, acetals etc. The one-pot tandem reac-
tion of hydroformylation along with the other transformation is
always advantageous over multistep synthesis since it avoids
the complex steps for the separation and purification of
aldehyde intermediates, which fulfills the principles of atom
economy and low energy consumption in green chemistry [5–7].
Examples include tandem hydroformylation–acetalization,
hydroformylation–hydrogenation, hydroformylation–aldol con-
densation etc. [2,8–17], in which tandem hydroformylation–acetali
zation represent a one-pot synthesis of acetals via formation of
aldehydes followed by the acetalization with alcohols. Acetals
could be used to protect the sensitive aldehyde group from side
reactions in organic synthesis or to further synthesize fine chemi-
cals such as pharmaceutical, fragrances, domestics, and detergents
[18–20]. As for tandem hydroformylation–acetalization, two types
catalytic systems are required wherein the phosphine-based tran-
sition metal catalyst is responsible for hydroformylation of olefins
produce acetals. In general, the phosphine-based transition metal
catalysts and the Lewis/ Brønsted acid catalysts are used in the
mode of mechanical mixing [20,22–24]. More recently, the bi-
functional phosphines dually containing phosphino-fragments
and Lewis acidic moieties (such as phosphonium) has been
explored by us for Rh(I)-catalyzed tandem hydroformylation-
acetalization of olefins with advantages of the bi-functional syner-
getic co-catalysis and the simplified manipulation without the
function-quenching problem [25,26]. On the other hand, the high
valence state transition metal compounds also can serve as the
bi-functional catalysts due to their ability to complex with the
electron-deficient ligands as well as the inherent Lewis acidic char-
acter [11,21,27,28]. For example, RhCl3Á3H2O could directly drive
tandem hydroformylation-acetalization of olefins with the
involvement of electron-deficient phosphites [P(OR)3][21]. And
the ionic electron-deficient diphosphine based RuCl3Á3H2O system
also proved to be catalytically bi-functional for tandem
hydroformylation-acetalization-hydrogenolysis in our previous
work [11]. The requirement of electron-deficient P-containing
ligands like phosphites or the ionic phosphines with intensive
p-
accepting nature is to warrant the high-valence state of the
metal-ion unchanged without redox between metal-ion (like
Rh3+/Ru3+) and the involved ligand. Resultantly, the corresponding
high-valence metal-catalyst was featured with two functionalities
⇑
Corresponding author.
E-mail address: yliu@chem.ecnu.edu.cn (Y. Liu).
https://doi.org/10.1016/j.jcat.2019.04.004
0021-9517/Ó 2019 Published by Elsevier Inc.

216
H. Liu et al. / Journal of Catalysis 373 (2019) 215–221
in terms of transition metal catalysis and Lewis acid catalysis
[11,29]. However, the lability of P–O bonds in phosphites towards
hydrolysis has limited their practical applications [30–32].
(Entry 1). And the additional introduction of anhydrous FeCl3 as
a Lewis acid co-catalyst under the same conditions successfully
led to the subsequent conversion of heptanals to the corresponding
acetals, resulting in 95% conversion of 1-hexene with 78% selectiv-
ity to acetals as well as 17% selectivity to hexane (Entry 2). How-
ever, the addition of H2O (10 mol%) into anhydrous FeCl3
(2.0 mol%) led to the decreased conversion of 1-hexene accompa-
nied by the boosted side-reaction of hydrogenation towards n-
hexane (Entries 3 vs 2), probably due to the hydrolysis of FeCl3
with the release of HCl. This comparison data indicated that the
low-valence Ir(I)-catalyst didn’t exhibit any activity toward the
acetalization of the aldehydes, which only transformed into the
acetals over the additional Lewis acid catalyst (FeCl3). Interestingly,
over L1-based IrCl3Á3H2O system, the conversion of 1-hexene
reached 96% along with 89% selectivity to the acetals (Entry 4).
Accordingly, L1-based IrCl3Á3H2O system served as an ideal bi-
functional catalyst not only catalyzing the hydroformylation of ole-
fin to produce aldehyde, but also effectively spurring the subse-
quent acetalization of the aldehydes with MeOH. It was also
noted that over L1-based IrCl3Á3H2O the conversion of 1-hexene
was even much higher than that over L1-based RhCl3Á3H2O catalyst
(Entry 5 vs 4) [40,41].
Knowingly, compared to the electron-withdrawing groups like
ACF3, ANO2 and ACOR, the positive-charged quaternary ammoni-
ums (such as imidazolium) are one of the most intensive electron-
withdrawing moieties. Hence, the linkage of imidazolium moiety
to P-atom can greatly decrease the electron-density of the resul-
tant phosphines [11,33–35]. On the other hand, the replacement
of phenyl ring of PPh3 by N-containing heteroaryl ring (such as imi-
dazolyl) also renders the corresponding phosphine the electron-
deficiency to some extent [25,36,37]. Herein, for the first time, a
series of imidazolyl- and imidazolium-tailed phosphines (L1-L6)
were applied, which were featured with the electron-deficient
character, in order to warrant the bi-functionalities of the high-
valence IrIII-catalyst to fulfill co-catalysis for one-pot tandem
hydroformylation-acetalization of olefins. Since IrIII-ion is a much
stronger Lewis acid in comparison to IrI-ion, it is believed that
the electron-deficient phosphine modified Ir(III)-complex is able
to serve as a bi-functional catalyst merging transition metal cata-
lyst (IrIII-P) and Lewis acid catalyst (Ir3+). In addition, as for the imi-
dazolium tailed phosphines (L2, L4 and L6), they are typical ionic
compounds with high polarity and improved stability against
water and oxygen, which can be used with the room temperature
ionic liquid (RTIL) solvent to fulfill the recovery and recycling of the
homogenous Ir-catalyst expectantly [38,39] (see Scheme 1).
Highlighted by the co-catalysis of L1-based IrCl3Á3H2O for tan-
dem hydroformylation-acetalization of 1-hexene, the ligand effect
on the catalytic performance of IrCl3Á3H2O precursor were carefully
investigated in Table 2.
L1-L4 were obtained respectively via the replacement of one
phenyl ring of PPh3 by imidazolyl- or imidazolium-group. And
the diphosphine analogues of L5 and L6 were also studied in par-
allel. The electronic nature of the phosphines of L1-L6 was evalu-
2. Results and discussion
The one-pot tandem hydroformalytion-acetalization of
1-hexene over the different catalyst precursors was initially inves-
tigated with the involvement of L1 as summarized in Table 1.
Under the optimal conditions [see S. Table 1 in ESI for screening
the reaction conditions], over L1-based [IrI(COD)Cl]2 system, only
hydroformylation occurred smoothly resulting in 82% conversion
of 1-hexene to heptanals with selectivity of 90% and L/B of 76/24
ated by the magnitude of
corresponding phosphine selenide [42,43] recorded by 31P NMR
spectroscopy (see ESI). An increase value of
1 31P–77Se indicates a
decrease of electron-density of P-atom and then an increase in
the character of -acceptor ability of the phosphine. In comparison,
L1-L6 are definitely more electron-deficient featured with more
J
1 31P–77Se coupling constant of the
J
p
Scheme 1. The phosphines (L1-L6) with electron-deficient character applied in IrCl3Á3H2O catalyzed hydroformylation-acetalization.

H. Liu et al. / Journal of Catalysis 373 (2019) 215–221
217
Table 1
The one-pot tandem hydroformylation-acetalization of 1-hexene over different catalyst precursors with involvement of L1.a
Entry
Precursor
Co-catalyst
Conv. (%)b
Sel. (%)b
L/Bb
Aldehydes
Acetals
n-Hexane
Isomer
1
[IrI(COD)Cl]2
[IrI(COD)Cl]2
[IrI(COD)Cl]2
IrIIICl3Á3H2O
RhIIICl3Á3H2O
–
82
95
82
96
63
90
<1
<1
<1
7
–
9
<1
4
7
<1
<1
76/24
78/22
74/26
78/22
62/38
2c
3d
4
FeCl3
FeCl3 + H2O
–
–
78
70
89
92
17
23
10
<1
5
a
Ir 0.01 mmol (0.2 mol%), L1 0.01 mmol (P/Ir = 1 M ratio), 1-hexene 5.0 mmol, methanol 5 mL, N-methyl pyrrolidone (NMP) 2 mL, CO/H2 (vCO:vH2 = 5:1) 4.0 MPa, tem-
perature 110 °C, time 8 h.
b
Determined by GC and GC-Mass; L/B, the ratio of linear aldehydes and acetals to branched aldehydes and acetals.
Anhydrous FeCl3 0.1 mmol (2.0 mol%).
Anhydrous FeCl3 0.1 mmol (2.0 mol%) and H2O 10 mL (10 mol%).
c
d
Table 2
IrCl3Á3H2O-catalyzed tandem hydroformylation-acetalization of 1-hexene in the presence of different phosphines.a
Entry
ligand
J
1 31P–77Se
Time (h)
Conv. (%)b
Sel. (%)b
L/Bb
TONc
Aldehydes
Acetals
n-Hexane
Isomer
1
2
3
4
5
6
7
8
–
L1
L2
L3
L4
L5
L6
L6
–
8
8
8
8
8
8
8
10
8
8
8
66
96
81
94
79
97
82
95
78
79
80
<1
<1
<1
<1
<1
<1
<1
<1
<1
<1
<1
73
89
86
88
87
92
87
87
79
85
86
26
10
13
11
12
7
12
12
20
14
13
<1
<1
<1
<1
<1
<1
<1
<1
<1
<1
<1
78/22
78/22
78/22
78/22
78/22
78/22
79/21
79/21
80/20
79/21
80/20
241
427
348
413
344
446
356
413
253
344
344
753[41]
780[41]
750
789
751[41]
782[41]
782[41]
729[41]
789
9
PPh3
L4
10d
11e
IrIII-L4
–-
a
b
c
IrCl3Á3H2O 0.01 mmol (Ir 0.2 mol%), P/Ir = 1 (molar ratio), 1-hexene 5.0 mmol, methanol 5 mL, NMP 2 mL, CO/H2 (vCO:vH2 = 5:1) 4.0 MPa, temperature 110 °C, time 8 h.
Determined by GC; L/B, the ratio of linear acetals to branched acetals.
TON, turnover number = mol of acetal products (mol of Ir)À1
P/Ir = 2 (molar ratio)f;
.
d
e
The as-synthesized IrIII-L4 complex was used.
p-accepting character than PPh3 (Table 2), in which the ionic L2, L4
and L6 are more electron-deficient than their counterparts. Evi-
dently, the absence of any phosphine led to the sluggish conversion
of 1-hexene to heptanals, which could rapidly transform into the
corresponding acetals over the unmodified IrCl3Á3H2O (Entry 1).
L1-L6 universally corresponded to much higher conversion of 1-
henexe and the better selectivity to the acetals than PPh3 (Entries
2–7 vs 9). It was found that the neutral phosphines (L1, L3 and L5)
universally led to the higher conversion of 1-hexene and the better
selectivity to the acetals than their ionic counterparts (L2, L4 and
L6) (Entries 2 vs 3; Entries 4 vs 5; Entries 6 vs 7). In particular, over
the neutral diphosphine of L5, the conversion of 1-hexene reached
97% along with 92% selectivity to the acetals, whereas its ionic
counterpart of L6 corresponded to 82% conv. and 87% sel. (Entries
6 vs 7). Certainly, the prolonged reaction time to 10 h could
increase the conversion of 1-hexene and yield of acetals over L6-
based IrCl3Á3H2O system (Entry 8). It was found that when the
as-synthesized IrIII-L4 was used to replace the physical mixtures
L4 and IrCl3Á3H2O at P/Ir of 2, nearly the same conversion of 1-
hexene along with the identical selectivity to the acetals was
observed under the same conditions, indicating the in situ formed
IrIII-L4 exhibited the same activity as the as-synthesized one (Entry
11 vs 10).
The available molecular structure (Fig. 1) of the complex of
IrIII-L4 obtained upon complexation of IrCl3Á3H2O with L4 further
confirmed that the use of an electron-deficient phosphine indeed
kept + 3 valence state of Ir-center unchanged. In IrIII-L4, the
IrIII-complex cation which is in an ideal octahedral geometry is
counteracted by one anionic PFÀ6 . The IrIII-center is six-
coordinated by four chlorine atoms in the equatorial plane and
two imidazolium-tailed phosphines in the axial positions. The
Fig. 1. The single crystal structure of IrIII-L4 (all H-atoms and solvent molecules
have been omitted for clarity). The selected bond distances (Å): Ir-P1 2.3639 (13),
Ir-Cl1 2.3602 (13), Ir-Cl2 2.3628 (12).
bond distances of P-IrIII is 2.3639 (13) Å identically, which are
relatively longer than the classical ones (2.29–2.32 Å) in the typical
phosphine-ligated IrI-complexes [41,44]. It is believed that the

218
H. Liu et al. / Journal of Catalysis 373 (2019) 215–221
reduction of IrIII to IrI unavoidably ensues with the presence of the
electron-rich donor like PPh3 as a good reducing reagent, leading to
the formation of IrI-complex finally in the course of complexation
of IrIII-ion with PPh3. Hence, the previous reported PPh3-ligated
IrIII-complexes were prepared with the involvement of risky oxi-
dant like SnOCl2 or liquid bromine [45,46]. In contrast, L4 is a very
electron-deficient phosphine with much weaker electron-donating
ability and then the dramatically weakened reductive ability. Con-
sequently, the redox reaction between L4 and IrCl3Á3H2O in the
course of complexation is avoided completely, leading to the avail-
ability of trivalence IrIII-L4.
In order to prove that Ir(III)-species were not reduced to Ir(I)
during the reaction procedures at 110 °C, the obtained reaction
mixture by using the as-synthesized IrIII-L4 as the catalyst was
detected by the 31P NMR spectroscopy (500 MHz). The obtained
spectra (Fig. 2C) showed that the characteristic peak for IrIII-L4
was still observed at À21.77 ppm which was consistent to the sig-
nal of the fresh sample of IrIII-L4 (Fig. 2B), whereas the signal at the
much lower field (d = 22.58 ppm) assigned to IrI-L4 complex was
unobservable completely. In addition, the characteristic peak of
the free ligand of L4 was also present at À29.02 ppm, indicating
the partial dissociation of L4 from IrIII-L4 to make accommodation
for the substrate (olefin and CO) insertion.
The scope of tandem hydroformylation-acetalization of olefins
with the alcohols catalyzed by L5-IrCl3Á3H2O system was explored
in Table 3. It was found that, as for the terminal aliphatic olefins,
the yields of products decreased with the increase of the carbon
chains (Entries 1–3). The internal olefin of 2-octene also gave the
high yield of the target acetals (81%) with L/B of 35/65 (Entry 4).
Cyclooctene and 2,5-dihydrofuran corresponded to the low yield
Fig. 2. A: The 31P NMR spectra of L4 (A), IrIII-L4 (B), the resultant mixture using IrIII
-
L4 as the catalyst (C) and IrI-L4 prepared by reacting [IrI(COD)Cl]2 with L4 in the
presence of CO (D).
Table 3
Generality of L5-based IrCl3Á3H2O for tandem hydroformylation-acetalization.a
Entry
1
Olefin
Alcohol
MeOH
Major product
Yieldacetals (%)b
89
L/Bb
78/22
2
MeOH
84
80/20
3
4
MeOH
MeOH
83
81
77/23
35/65
5
MeOH
62
–
6
MeOH
MeOH
11
80
–
7c
31/69
8c
9c
MeOH
MeOH
81
81
33/67
32/68
10c
11c
12c
MeOH
MeOH
MeOH
79
76
73
31/69
30/70
25/75
13
14
EtOH
80
78
80/20
85/15
i-PrOH
15
Ethylene glycol
88
75/25
a
IrCl3Á3H2O 0.01 mmol (Ir 0.2 mol%), L5 0.005 mmol (P/Ir = 1 M ratio), 1-hexene 5.0 mmol, methanol 5 mL, N-methyl pyrrolidone (NMP) 2 mL, CO/H2 (vCO:vH2 = 5:1)
4.0 MPa, time 8 h, temperature 110 °C.
b
Determined by GC and GC–MS; L/B, the ratio of linear acetals to branched acetals.
IrCl3Á3H2O 0.05 mmol (Ir 1 mol%), L5 0.025 mmol, 14 h.
c

H. Liu et al. / Journal of Catalysis 373 (2019) 215–221
219
to guarantee the Lewis acidity of IrIII-center, which was verified by
the available molecular structure of IrIII-L4. It was found that L5-
based IrCl3Á3H2O exhibited the best performance for this tandem
reaction, affording 97% conversion of 1-hexene along with 92%
selectivity to the corresponding acetals. In addition, the stable
and ionic L6-based IrCl3Á3H2O system could be successfully recy-
cled at least 6 times in the IL of [Bmim]PF6.
4. Experimental
4.1. Reagents and analysis
The terminal aliphatic olefins, alcohols, FeCl3 and [Bmim]PF6
were purchased from Shanghai Aladdin Bio-Chem Technology
Co., LTD. The compounds of [Ir(COD)Cl]2, IrCl3Á3H2O, and
RhCl3Á3H2O were purchased from Shanghai Boka-chem Tech Inc..
Styrene and its derivatives were purchased from Alfa Aesar China.
The solvents were distilled and dried before use. The 1H and 31P
NMR spectra were recorded on a Bruker Avance 500 spectroscopy.
The 31P NMR spectra were referenced to 85% H3PO4 sealed in a cap-
illary tube as an internal standard. CHN-Elemental analyses were
obtained using an Elementar Vario EL III instrument. Gas chro-
matography (GC) was performed on a SHIMADZU-2014 equipped
Fig. 3. The recycling uses of the L6-IrCl3Á3H2O catalytic system in [Bmin]PF6 for
biphasic hydroformylation-acetalization of 1-hexene [IrCl3Á3H2O 0.01 mmol (Ir
0.2 mol%), L6 0.005 mmol (P/Ir = 1 M ratio), 1-hexene 5.0 mmol, methanol 5 mL,
[Bmim]PF6 2 mL, CO/H2 (vCO:vH2 = 5:1) 4.0 MPa, time 15 h, temperature 110 °C].
of the acetals due to the bulky steric hindrance (Entries 5 and 6).
When styrene and its derivatives were applied to repeat the reac-
tions at the prolonged time of 14 h, the good yields of the
corresponding acetals (73–80%) were obtained (Entries 7–12).
When EtOH was applied instead of MeOH, the tandem
hydroformylation-acetalization of 1-hexene performed smoothly
with 80% yield to the acetals (Entry 13). The increased steric hin-
drance of i-PrOH slightly slowed down the reaction rate (Entry
14). Ethylene glycol corresponded to a much higher yield of the
acetals (88%) due to the formation of a thermodynamically stable
five-membered 1,3-dioxolanyl ring (Entry 15).
with a DM-Wax capillary column (30 m  0.25 mm  0.25
The analyses of GC-Mass (GC–MS) equipped with a DB-Wax capil-
m) was determined on an
lm).
lary column (30 m  0.25 mm  0.25
l
Agilent 6890 instrument equipped with an Agilent 5973 mass
selective detector. The amount of Ir and P in the organic phase
was quantified by using an inductively coupled plasma optical
emission spectrometer (ICP-OES) on an Optima 8300 instrument
(PE Corporation).
4.2. Synthesis
In addition, it has been well known that the ionic phosphines
which possess the advantages of good stability and high polarity
can be applied together with room temperature ionic liquid (RTIL)
to immobilize the homogeneous transition metal catalysts for
recovery and recycling [10,41,47]. Herein, L6 and IrCl3Á3H2O were
dissolved in the room temperature ionic liquid of [Bmim]PF6 after
comparison to that in [Bmim]BF4, [Bmim]NTf2 and [PEmim]PF6
(S. Table 2 in ESI), in order to lock the ionic L6-based IrCl3Á3H2O cat-
alyst in the IL phase for the recovery and recycling. It was indicated
in Fig. 3, L6-based IrCl3Á3H2O could be recycled 6 runs. The gradual
decrease of 1-hexene conversion was mainly due to the physical loss
of the catalyst during the transfer process. The precipitation of metal
blacks was never observed during the recycling. The ICP-OES analy-
sis revealed that the leaching of Ir and P in the combined organic
phase was non-detectable after 6 runs (below the detection limit
The phosphines of L1-L6 were prepared according to the proce-
dures reported by our group previously [41,44,48].
4.2.1. Complex IrIII-L4
Under nitrogen atmosphere, L4 (1.0 mmol) dissolved in 10 mL
of dry MeOH was added to the solution containing IrCl3Á3H2O
(0.2 mmol)
and
tetrabutylammonium
chloride
(Bu4NCl,
0.17 mmol) in MeOH. The resultant mixture was refluxed for
12 h under vigorous stirring. After cooling to room temperature,
the yellow precipitate was collected after washing with methanol
and diethyl ether respectively, and then dried under vacuum to
give the product of IrIII-L4 (Yield: 52%). A sample suitable for the
single crystal X-ray diffraction analysis was obtained by recrystal-
lization from methanol/ethyl ether. 1H NMR [d, ppm, (CD3)2CO,
298 K]: 8.68 (br, 4H), 8.05 (s, 1H), 7.95 (s, 1H), 7.51(m, 2H), 7.45
(m, 4H), 3.92 (br, 2H), 3.78 (s, 3H), 1.95 (br, 2H), 1.05 (br, 2H),
0.72 (s, 3H). 31P NMR [d, ppm, (CD3)2CO, 298 K]: À21.55 (br),
À145.08 (PFÀ6 , heptet). CHN-Elemental analysis (calculated, %): C
43.09 (42.68), H 4.77 (4.30), N 4.51 (4.98).
of <0.1 lg/g). However, the use of [Bmim]PF6 as the solvent led to
the biphasic reaction system with mass transfer limitation. So, the
reaction time was prolonged to 15 h in comparison to that (8 h) in
the homogenous system (Entry 6 of Table 2).”
3. Conclusions
4.2.2. Complex IrI-L4
IrCl3Á3H2O with the involvement of the electron-deficient phos-
phines (L1-L6) proved to be the efficient bi-functional catalyst to
fulfill co-catalysis for one-pot tandem hydroformylation-acetaliza
tion, which not only served as a transition metal catalyst responsi-
ble for hydroformylation of olefins, but also as an IrIII-Lewis acid
catalyst in charge of acetalization of aldehydes. The measurement
Under nitrogen atmosphere, a solution of [Ir(COD)Cl]2 [dimer of
dichloro(1,5-cyclooctadiene)iridium(I), 0.05 mmol] in absolute
dichloromethane (10 mL, refluxed with calcium hydride and dis-
tilled freshly before use) was stirred vigorously at room tempera-
ture for 10 min, and then the atmospheric CO (in a balloon) was
introduced into the reaction mixture for 50 min. The obtained mix-
ture was treated with a solution of L4 (0.05 mmol) in acetonitrile
(5 mL) and stirred vigorously for 12 h. Then diethyl ether was
added to afford the yellow precipitates, which were collected after
drying under vacuum with the yield of 22%. 1H NMR (500 MHz, d,
of J
1 31P–77Se indicated that the electron-deficient character of
these phosphines were in the ranking of L2, L4, L6 > L1, L3,
L5 > PPh3. Resultantly, +3 valence state of IrIII-ion could be kept
without reduction during the complexation with these phosphines

220
H. Liu et al. / Journal of Catalysis 373 (2019) 215–221
ppm, CD3CN): 8.03 (m, 8H), 7.86 (m, 4H), 7.68 (m, 8H), 7.58 (m,
4H), 3.80 (t, 4H), 3.57 (s, 6H), 1.51 (m, 4H), 0.96 (m, 4H), 0.72 (t,
6H). 31P NMR (202 MHz, d, ppm, CD3CN): 22.58 (s, PPh2),
À143.72 (PFÀ6 , heptet). CHN-Elemental analysis (calculated, %): C
42.23 (41.30), H 4.36 (4.06), N 4.32 (4.70).
Upon completion, the reaction solution was added with n-hexane
(20 mL). Then the upper organic phase was decanted from the
obtained biphasic reaction mixture, and the remaining IL phase
was washed with n-hexane (3 mL Â 3) to completely extract the
reactants and products. The combined organic phase was analyzed
by GC and ICP-OES. The IL phase containing the catalyst after the
dryness under vacuum was reused for the next run.
4.3. X-ray crystallography
The intensity data for IrIII-L4 was collected on a Bruker SMAR-
Acknowledgements
TAPEX II diffractometer using graphite monochromated Mo-K
a
This work was financially supported by the National Natural
Science Foundation of China (Nos. 21673077 and 21473058), and
the Science and Technology Commission of Shanghai Municipality
(18JC1412100).
radiation (k = 0.71073 Å). Data reduction included absorption cor-
rections by the multi-scan method. The structures were solved
by direct methods and refined by full matrix least-squares using
SHELXS-97 (Sheldrick, 1990), with all non-hydrogen atoms refined
anisotropically. Hydrogen atoms were added at their geometrically
ideal positions and refined isotropically. The crystal data and
refinement details are given in Table 4.
Appendix A. Supplementary material
Supplementary data to this article can be found online at
https://doi.org/10.1016/j.jcat.2019.04.004.
4.4. General procedures for tandem hydroformylation-acetalization of
olefins
References
The following general procedure was considered for 1-hexene
adopted as a model substrate. A mixture of N-methyl pyrrolidone
(NMP) 2 mL (solvent), IrCl3Á3H2O (0.01 mmol Ir 0.2 mol %), the
phosphine (P/Ir = 1 M ratio), 1-hexene (or the other olefin,
5.0 mmol) and MeOH (5 mL, or other alcohol) were added sequen-
tially in a 50 mL sealed Teflon-lined stainless steel autoclave. The
autoclave was purged with H2 (0.5 MPa) for three times, and then
pressured by H2 (0.7 MPa) and CO (3.3 MPa) respectively. The reac-
tion mixture was stirred vigorously at the appointed temperature
for some time. Upon completion, the autoclave was cooled down
to room temperature and slowly depressurized. The solution was
analyzed by GC to determine the conversion (n-dodecane as inter-
nal standard) and the selectivity (normalization method). And the
products were further identified by GC-Mass analysis.
[1] R. Franke, D. Selent, A. Börner, Applied hydroformylation, Chem. Rev. 112
(2012) 5675–5732, https://doi.org/10.1021/cr3001803.
[2] K. Takahashi, M. Yamashita, K. Nozaki, Tandem hydroformylation/
hydrogenation of alkenes to normal alcohols using Rh/Ru dual catalyst or Ru
single component catalyst, J. Am. Chem. Soc. 134 (2012) 18746–18757, https://
doi.org/10.1021/ja307998h.
[3] J. Pospech, I. Fleischer, R. Franke, S. Buchholz, M. Beller, Alternative metals for
homogeneous catalyzed hydroformylation reactions, Angew. Chem. Int. Ed. 52
(2013) 2852–2872, https://doi.org/10.1002/anie.201208330.
[4] I. Piras, R. Jennerjahn, R. Jackstell, A. Spannenberg, R. Franke, M. Beller, A
general and efficient iridium-catalyzed hydroformylation of olefins, Angew.
Chem. Int. Ed. 50 (2011) 280–284, https://doi.org/10.1002/anie.201001972.
[5] J.-C. Wasilke, S.J. Obrey, R.T. Baker, G.C. Bazan, Concurrent tandem catalysis,
Chem. Rev. 105 (2005) 1001–1020, https://doi.org/10.1021/cr020018n.
[6] D.E. Fogg, E.N. dos Santos, Tandem catalysis: a taxonomy and illustrative
review, Coord. Chem. Rev. 248 (2004) 2365–2379, https://doi.org/10.1016/j.
ccr.2004.05.012.
[7] M.J. Climent, A. Corma, S. Iborra, Heterogeneous catalysts for the one-pot
synthesis of chemicals and fine chemicals, Chem. Rev. 111 (2011) 1072–1133,
https://doi.org/10.1021/cr1002084.
[8] P. Eilbracht, L. Bärfacker, C. Buss, C. Hollmann, B.E. Kitsos-Rzychon, C.L.
Kranemann, T. Rische, R. Roggenbuck, A. Schmidt, Tandem reaction sequences
under hydroformylation conditions: new synthetic applications of transition
metal catalysis, Chem. Rev. 99 (1999) 3329–3366, https://doi.org/10.1021/
cr970413r.
[9] G. Parrinello, J.K. Stille, Asymmetric hydroformylation catalyzed by
homogeneous and polymer-supported platinum complexes containing chiral
phosphine ligands, J. Am. Chem. Soc. 109 (1987) 7122–7127, https://doi.org/
10.1021/ja00257a036.
As for the catalyst recycling experiments, IrCl3Á3H2O
(0.01 mmol Ir 0.2 mol %), L6 (0.005 mmol, P/Ir = 1 M ratio), 1-
hexene (5.0 mmol), MeOH (5 mL), and [Bmim]PF6 (2 mL) were
sequentially added in a 50 mL sealed Teflon-lined stainless steel
autoclave which was purged with H2 (0.5 MPa) for three times,
and then pressured by H2 (0.7 MPa) and CO (3.3 MPa) respectively.
The mixture was stirred at 110 °C for 15 h in the sealed autoclave.
Table 4
[10] Y.-Q. Li, Q. Zhou, D.-L. Wang, P. Wang, Y. Lu, Y. Liu, Co-catalysis for one-pot
The crystal data and structure refinement for IrIII-L4.
tandem
hydroformylation-aldol
condensation-hydrogenation
with
IrIII-L4
involvement of phosphino-phosphonium based bi-functional ligand and
aniline, Mol. Catal. 439 (2017) 25–30, https://doi.org/10.1016/j.
mcat.2017.06.019.
Empirical formula
Formula weight
Crystal system
Space group
a (Å)
C
40H48Cl4Ir1N4P2Á(P1F6)Á2(C3H6O1)
1241.88
Monoclinic
C 2/c
[11] P. Wang, D.-L. Wang, H. Liu, X.-L. Zhao, Y. Lu, Y. Liu, Production of alcohols from
olefins via one-pot tandem hydroformylation–acetalization–hydrogenolysis
III
over bifunctional catalyst merging Ru III–P complex and Ru
lewis acid,
Organometallics 36 (2017) 2404–2411, https://doi.org/10.1021/acs.
organomet.7b00266.
25.2852(12)
9.7142(5)
22.8565(11)
90
104.2900(10)
90
5440.4(5)
4
1.516
b (Å)
c (Å)
[12] L. Wu, I. Fleischer, R. Jackstell, I. Profir, R. Franke, M. Beller, Ruthenium-
catalyzed hydroformylation/reduction of olefins to alcohols: extending the
scope to internal alkenes, J. Am. Chem. Soc. 135 (2013) 14306–14312, https://
doi.org/10.1021/ja4060977.
[13] I. Fleischer, K.M. Dyballa, R. Jennerjahn, R. Jackstell, R. Franke, A. Spannenberg,
M. Beller, From olefins to alcohols: efficient and regioselective ruthenium-
catalyzed domino hydroformylation/reduction sequence, Angew. Chem. Int.
Ed. 52 (2013) 2949–2953, https://doi.org/10.1002/anie.201207133.
[14] S. Gülak, L. Wu, Q. Liu, R. Franke, R. Jackstell, M. Beller, Phosphine- and
a
(°)
b (°)
c
(°)
V (Å3)
Z
dcalc (g cmÀ3
)
l
(Mo-K ) (mmÀ1
)
2.789
a
T (K)
296(2)
hydrogen-free:
highly
regioselective
ruthenium-catalyzed
hydroaminomethylation of olefins, Angew. Chem. Int. Ed. 53 (2014) 7320–
7323, https://doi.org/10.1002/anie.201402368.
[15] X. Fang, R. Jackstell, A. Börner, M. Beller, Domino hydroformylation/aldol
condensation/hydrogenation catalysis: highly selective synthesis of ketones
from olefins, Chem. – Eur. J. 20 (2014) 15692–15696, https://doi.org/10.1002/
chem.201404294.
k (A)
0.71073
30,517
4769(0.0408)
0.0323
0.0846
2496.0
Total reflections
Unique reflections (Rint
R1 [I > 2 (I)]
)
r
wR2 (all data)
F(0 0 0)
[16] J. Liu, C. Kubis, R. Franke, R. Jackstell, M. Beller, From internal olefins to linear
Goodness-of-fit on F2
1.072
amines:
ruthenium-catalyzed
domino
water-gas
shift/

H. Liu et al. / Journal of Catalysis 373 (2019) 215–221
221
hydroaminomethylation sequence, ACS Catal. 6 (2016) 907–912, https://doi.
org/10.1021/acscatal.5b02457.
[34] S. Jeulin, S. Duprat de Paule, V. Ratovelomanana-Vidal, J.-P. Genêt, N.
Champion, P. Dellis, Difluorphos, an electron-poor diphosphane: good
a
[17] L. Wu, I. Fleischer, R. Jackstell, M. Beller, Efficient and regioselective
ruthenium-catalyzed hydro-aminomethylation of olefins, J. Am. Chem. Soc.
135 (2013) 3989–3996, https://doi.org/10.1021/ja312271c.
[18] C.G. Vieira, J.G. da Silva, C.A.A. Penna, E.N. dos Santos, E.V. Gusevskaya, Tandem
hydroformylation-acetalization of para-menthenic terpenes under non-acidic
conditions, Appl. Catal. Gen. 380 (2010) 125–132, https://doi.org/10.1016/j.
apcata.2010.03.045.
match between electronic and steric features, Angew. Chem. Int. Ed. 43
(2004) 320–325, https://doi.org/10.1002/anie.200352453.
[35] M.L. Clarke, D. Ellis, K.L. Mason, A.G. Orpen, P.G. Pringle, R.L. Wingad, D.A.
Zaher, R.T. Baker, The electron-poor phosphines P{C6H3(CF3), 2–3,5}3 and
P(C6F5)3 do not mimic phosphites as ligands for hydroformylation.
comparison of the coordination chemistry of P{C6H3(CF3)2–3,5}3 and P(C6F5)
and the unexpectedly low hydroformylation activity of their rhodium
A
3
[19] B. El Ali, J. Tijani, M. Fettouhi, Rh(I) or Rh(III) supported on MCM-41-catalyzed
selective hydroformylation–acetalization of aryl alkenes: effect of the
additives, Appl. Catal. Gen. 303 (2006) 213–220, https://doi.org/10.1016/j.
apcata.2006.02.004.
[20] X. Jin, K. Zhao, F. Cui, F. Kong, Q. Liu, Highly effective tandem
hydroformylation–acetalization of olefins using a long-life Brønsted acid–Rh
bifunctional catalyst in ionic liquid–alcohol systems, Green Chem. 15 (2013)
3236, https://doi.org/10.1039/c3gc41231h.
[21] B. El Ali, J. Tijani, M. Fettouhi, Selective hydroformylation–acetalization of aryl
alkenes in methanol catalyzed by RhCl3Á3H2O–P(OPh)3 system, J. Mol. Catal.
Chem. 230 (2005) 9–16, https://doi.org/10.1016/j.molcata.2004.12.005.
[22] K. Soulantica, S. Sirol, S. Koïnis, G. Pneumatikakis, P. Kalck, Direct synthesis of
acetals by rhodium catalysed hydroformylation of alkenes in the presence of
orthoformate, J. Organomet. Chem. 498 (1995) C10–C13, https://doi.org/
10.1016/0022-328X(95)05594-F.
[23] E. Fernández, S. Castillón, Synthesis of acetals from alkenes by one-pot
hydroformylation-transacetalization reactions catalysed by rhodium
complexes and pyridinium p-toluenesulphonate, Tetrahedron Lett. 35 (1994)
2361–2364, https://doi.org/10.1016/0040-4039(94)85220-0.
[24] J. Norinder, C. Rodrigues, A. Börner, Tandem hydroformylation–acetalization
with a ruthenium catalyst immobilized in ionic liquids, J. Mol. Catal. Chem.
391 (2014) 139–143, https://doi.org/10.1016/j.molcata.2014.04.009.
[25] P. Wang, H. Liu, Y.-Q. Li, X.-L. Zhao, Y. Lu, Y. Liu, Phosphonium-based
aminophosphines as bifunctional ligands for sequential catalysis of one-pot
hydroformylation–acetalization of olefins, Catal. Sci. Technol. 6 (2016) 3854–
3861, https://doi.org/10.1039/C5CY01827G.
[26] Y.-Q. Li, P. Wang, H. Liu, Y. Lu, X.-L. Zhao, Y. Liu, Co-catalysis of a bi-functional
ligand containing phosphine and Lewis acidic phosphonium for
hydroformylation–acetalization of olefins, Green Chem. 18 (2016) 1798–
1806, https://doi.org/10.1039/C5GC02127H.
[27] M.C. de Freitas, C.G. Vieira, E.N. dos Santos, E.V. Gusevskaya, Synthesis of
fragrance compounds from biorenewables: tandem hydroformylation-
acetalization of bicyclic monoterpenes, ChemCatChem 5 (2013) 1884–1890,
https://doi.org/10.1002/cctc.201200948.
[28] Z. Huang, Y. Cheng, X. Chen, H.-F. Wang, C.-X. Du, Y. Li, Regioselectivity
inversion tuned by iron(III) salts in palladium-catalyzed carbonylations, Chem.
Commun. 54 (2018) 3967–3970, https://doi.org/10.1039/C8CC01190G.
[29] Y. Yan, Y. Chi, X. Zhang, Novel phosphine-phosphite and phosphine-
phosphinite ligands for highly enantioselective asymmetric hydrogenation,
Tetrahedron Asymmetry 15 (2004) 2173–2175, https://doi.org/10.1016/j.
tetasy.2004.04.013.
complexes, Dalton Trans. 1294 (2005), https://doi.org/10.1039/b418193j.
[36] D. Yang, H. Liu, D.-L. Wang, Y. Lu, X.-L. Zhao, Y. Liu, Au-complex containing
phosphino and imidazolyl moieties as a bi-functional catalyst for one-pot
synthesis of pyridine derivatives, J. Mol. Catal. Chem. 424 (2016) 323–330,
https://doi.org/10.1016/j.molcata.2016.09.008.
[37] C. Tan, P. Wang, H. Liu, X.-L. Zhao, Y. Lu, Y. Liu, Bifunctional ligands in
combination with phosphines and Lewis acidic phospheniums for the
carbonylative Sonogashira reaction, Chem. Commun. 51 (2015) 10871–
10874, https://doi.org/10.1039/C5CC03697F.
[38] Y.-H. Chang, I. Tanigawa, H. Taguchi, K. Takeuchi, F. Ozawa, Iridium(I)
complexes bearing a noninnocent PNP-pincer-type phosphaalkene ligand:
catalytic application in the base-free N -alkylation of amines with alcohols: Ir
(I) complexes bearing a noninnocent phosphaalkene ligand, Eur. J. Inorg.
Chem. 2016 (2016) 754–760, https://doi.org/10.1002/ejic.201500900.
[39] Y.-H. Chang, Y. Nakajima, F. Ozawa, A Bis(phosphaethenyl)pyridine complex of
iridium(I): synthesis and catalytic application to N -alkylation of amines with
alcohols, Organometallics 32 (2013) 2210–2215, https://doi.org/10.1021/
om4000743.
[40] L. Wang, J.R. Sowa, C. Wang, R.S. Lu, P.G. Gassman, T.C. Flood, XPS
investigations of (1,4,7-trimethyl-1,4,7-triazacyclononane)RhMe3 and [1,1,1-
tris((dimethylphosphino)methyl)ethane]RhMe3 and Their RhÀC cleavage
derivatives. Comparison of hard- and soft-ligated rhodium organometallics,
Organometallics 15 (1996) 4240–4246, https://doi.org/10.1021/om9601099.
[41] H. Liu, D.-L. Wang, X. Chen, Y. Lu, X.-L. Zhao, Y. Liu, Efficient and recyclable Ir
(I)-catalysts with the involvement of p-acceptor phosphines for N-alkylation
of aryl amines with alcohols, Green Chem. 19 (2017) 1109–1116, https://doi.
org/10.1039/C6GC03096C.
[42] B. Blank, S. Michlik, R. Kempe, Synthesis of selectively mono-N-arylated
aliphatic diamines via Iridium-catalyzed amine alkylation, Adv. Synth. Catal.
351 (2009) 2903–2911, https://doi.org/10.1002/adsc.200900548.
[43] S. Michlik, R. Kempe, New iridium catalysts for the efficient alkylation of
anilines by alcohols under mild conditions, Chem. – Eur. J. 16 (2010) 13193–
13198, https://doi.org/10.1002/chem.201001871.
[44] H. Zhang, Y.-Q. Li, P. Wang, Y. Lu, X.-L. Zhao, Y. Liu, Effect of positive-charges in
diphosphino-imidazolium salts on the structures of Ir-complexes and catalysis
for hydroformylation, J. Mol. Catal. Chem. 411 (2016) 337–343, https://doi.org/
10.1016/j.molcata.2015.11.005.
[45] J. Cartwright, A.F. Hill, Oxidative addition of seleninyl chloride to Vaska’s
complex, Polyhedron 15 (1996) 157–159, https://doi.org/10.1016/0277-5387
(95)00083-5.
[46] M.A. Bennett, R.J.H. Clark, D.L. Milner, Far-infrared spectra of complexes of
[30] Y. Canac, N. Debono, L. Vendier, R. Chauvin, NHC-derived bis
(amidiniophosphine) ligands of Rh(I) complexes: versatile cisÀtrans
chelation driven by an interplay of electrostatic and orbital effects, Inorg.
Chem. 48 (2009) 5562–5568, https://doi.org/10.1021/ic900348x.
[31] H. Tricas, O. Diebolt, P.W.N.M. van Leeuwen, Bulky monophosphite ligands for
ethene hydroformylation, J. Catal. 298 (2013) 198–205, https://doi.org/
10.1016/j.jcat.2012.11.031.
rhodium and iridium with p-bonding ligands, Inorg. Chem. 6 (1967) 1647–
1652, https://doi.org/10.1021/ic50055a008.
[47] D. Yang, H. Liu, D.-L. Wang, Z. Luo, Y. Lu, F. Xia, Y. Liu, Co-catalysis over a bi-
functional ligand-based Pd-catalyst for tandem bis-alkoxycarbonylation of
terminal alkynes, Green Chem. 20 (2018) 2588–2595, https://doi.org/10.1039/
C8GC00754C.
[48] H. You, Y. Wang, X. Zhao, S. Chen, Y. Liu, Stable ionic Rh(I, II, III) complexes
[32] P.W.N.M. van Leeuwen, J.C. Chadwick, Homogeneous catalysts: activity,
stability, deactivation, Wiley -VCH, Weinheim, Germany, 2011.
[33] C.L. Pollock, G.C. Saunders, E.C.M.S. Smyth, V.I. Sorokin, Fluoroarylphosphines
as ligands, J. Fluor. Chem. 129 (2008) 142–166, https://doi.org/10.1016/j.
jfluchem.2007.11.003.
ligated by an imidazolium-substituted phosphine with p-acceptor character:
synthesis. Characterization, and application to hydroformylation,
Organometallics 32 (2013) 2698–2704, https://doi.org/10.1021/om400171t.